TOKYO — Japan ordered the release of 12 million barrels from its national petroleum stockpile on Saturday and opened a joint emergency-supply working group with South Korea, marking the most coordinated response by Northeast Asia’s two largest energy importers since the Iran war began.

The decision, announced after a brief cabinet-level meeting at the prime minister’s office in Nagatacho, authorized the Ministry of Economy, Trade and Industry to begin tendering the barrels to domestic refiners as early as Monday. METI Minister Ken Saito said the release would be drawn from the state-held portion of Japan’s roughly 480-million-barrel reserve — the world’s third-largest after the U.S. Strategic Petroleum Reserve and China’s holdings — and would be replaced over the second half of the year when market conditions allow.

“This is not a price-control measure,” Saito told reporters at a Saturday evening briefing. “It is a stability measure. We are sending a clear signal to households, to industry and to international markets that supply will be assured.”

The release was timed to coincide with a parallel announcement in Seoul, where the South Korean Ministry of Trade, Industry and Energy said it would draw down 7.5 million barrels from its own reserves and would suspend the consumption-tax surcharge on diesel and kerosene for an additional 90 days. The two governments said in a joint statement issued by the Japanese embassy in Seoul that they had agreed to “synchronized actions” and would convene a senior officials’ working group at vice-ministerial level beginning Monday in Tokyo.

Both economies depend on Persian Gulf crude for the majority of their imports — about 95 percent in Japan’s case and roughly 70 percent in South Korea’s — and both have spent the past five weeks scrambling to lock in additional cargoes from the United States, West Africa and the eastern Mediterranean. Tanker-tracking data compiled by Vortexa showed Japanese refiners had nominated a record 38 U.S. Gulf Coast liftings for May, more than double the average for the same period in 2025.

“Tokyo has been quietly absorbing the cost of this war since early March,” said Hiroshi Nakamura, chief energy economist at Nomura Securities in Tokyo. “What changed this week is the realization that the cost is no longer just financial. There are real questions about whether certain medium-sour grades will physically arrive on schedule in May. A reserve release was inevitable. The fact that it is being done jointly with Seoul is the more interesting development.”

The coordination marks a continuation of the cautious thaw between Tokyo and Seoul that began under the previous Japanese and South Korean administrations, and which both current governments have sought to preserve despite the more nationalist tone of their domestic coalitions. Prime Minister Sanae Takaichi, who succeeded Fumio Kishida last autumn, spoke by phone with South Korean President Lee Jae-myung on Friday evening, according to officials in both capitals. The call lasted roughly 40 minutes and covered the supply situation as well as a joint approach to the next G7 finance ministers’ meeting later this month.

Japanese gasoline at the pump averaged 198 yen per liter this week, up from 162 yen at the start of the year, according to the Oil Information Center. The price level has begun to bleed into broader consumer sentiment, with the Bank of Japan’s quarterly Tankan survey, released Friday, showing a sharp drop in confidence among small and medium-sized manufacturers. Two LDP lawmakers from energy-intensive Aichi prefecture had publicly called this week for an immediate stockpile release, and Saturday’s announcement was widely read in Tokyo as a response to that political pressure as much as to market signals.

In Seoul, the announcement was complicated by simmering domestic debate over the country’s nuclear-restart program. President Lee, who campaigned partly on accelerating reactor restarts paused under his predecessor’s energy plan, used Saturday’s joint statement to renew the case for “diversification of the energy mix away from imported hydrocarbons.” Officials at the energy ministry said two additional reactors at the Hanul complex on the east coast would return to service ahead of schedule by mid-May, adding roughly 2.4 gigawatts of baseload capacity.

The Northeast Asian moves come on top of a coordinated 60-million-barrel release announced last week by the International Energy Agency, and follow Tuesday’s OPEC+ decision in Vienna to add 1.5 million barrels a day to production through the second quarter. Brent crude has eased from a war-peak above $125 to settle near $107 on Friday, but futures curves remain in steep backwardation, signaling that traders expect near-term tightness even if a negotiated end to the fighting comes into view.

“The math for Asian refiners is brutal,” said Aileen Park, a Singapore-based downstream analyst at Wood Mackenzie. “Spot premiums on Murban and other Gulf grades are still elevated, the Hormuz insurance surcharge is real, and the alternative barrels from the Atlantic Basin take five to six weeks to arrive. A reserve release buys time. It does not fix the underlying problem, which is that the war has to end.”

Elsewhere in Asia, the Japanese and South Korean announcements drew measured responses. India’s petroleum ministry said it was “monitoring the situation” and had no immediate plans to tap its own much smaller reserves. Taiwan’s CPC Corp said it had secured sufficient cargoes through May. Chinese state media gave the Tokyo announcement modest play, with the Global Times noting that Japan’s release was “consistent with IEA member obligations” and avoiding the sharper criticism Beijing has directed at U.S. policy in recent days.

Japanese officials said a further tranche of reserve barrels could be authorized within two weeks if Gulf supply disruptions persisted, and that consultations with European and U.S. counterparts on a possible second coordinated IEA action would continue through the weekend.